1. Field of the Invention
The present invention relates to an optical pickup and an optical disc apparatus, and is preferably applied to an optical disc apparatus including an optical pickup in which a laser diode and a light detector are closely disposed or in which a laser diode and a beam splitter are closely disposed, for example.
2. Description of Related Art
An optical pickup is usually equipped with a laser diode. The laser diode is selected such that its rating is appropriate for recording: recording of information may require more intense emission light than reproduction of information.
The optical pickup may need to dramatically decrease the output power of the laser diode when reproducing information, to reduce the intensity of the emission light. However, decreasing the output power of the laser diode increases noise levels compared to the intensity of the optical beam emitted.
Accordingly, Patent Document 1 (Jpn. Pat. Laid-open Publication No. 2002-260272) discloses an optical pickup 1 equipped with a tunable filter 2 as shown in FIG. 1. The tunable filter 2 includes a high transmission section with substantially 100% transmission and a neutral density filter section that shuts down part of the optical beam. When recording information, the optical pickup 1 uses the high transmission section through which the optical beam passes, to increase the intensity of the emission light. When reproducing information, the optical pickup 1 uses the neutral density filter section through which the optical beam passes, to decrease the intensity of the emission light. This allows the optical pickup 1 to use the high-power laser diode even when reproducing information. The noise level is therefore well controlled.
The optical pickup 1 includes a laser diode 11 and a beam splitter 17. The tunable filter 2 is placed between the laser diode 11 and the beam splitter 17. During the reproduction process, the optical beam 40 emitted from the laser diode 11 passes through the neutral density filter section of the tunable filter 2. This decreases the intensity of the optical beam 40. A reflection optical beam 50, a beam reflected on an optical disc 100 changes its direction in the beam splitter 17 and reaches a light detector 22 without passing through the tunable filter 2. Accordingly, the intensity of the reflection optical beam 50 is not reduced.